Dielectric thin films play an important role in achieving desired performance of electronic and optoelectronic devices. Dense, closely packed thin films are required to protect the surface of semiconductor devices from contamination and oxidation. Dielectric thin films providing particular properties at the dielectric/semiconductor interface, such as low interface state density, are required in metal/insulator/semiconductor structures, and for laser facet or light-emitting device coatings.
In the case of electronic and optoelectronic III-V or II-VI semiconducting devices, a variety of materials has been proposed for such thin surface films including Al.sub.2 O.sub.3, SiO.sub.x, SiN.sub.x, ZrO.sub.2 and gallium oxide. The Al.sub.2 O.sub.3, SiO.sub.x, SiN.sub.x, and ZrO.sub.2 thin films were fabricated with dielectric properties and provide an encapsulation layer for surface protection. The midgap interface state density is in the 10.sup.13 cm.sup.-2 eV.sup.-1 range when deposited on bare GaAs samples and can be reduced to about 10.sup.12 cm.sup.-2 eV.sup.-1 when deposited on GaAs samples previously treated by dry or liquid surface passivation techniques. Gallium oxide thin films with dielectric properties have not been reported yet. Gallium oxide thin films deposited in an oxygen radio frequency plasma in a vacuum system, in conjunction with a GaAs surface previously treated by H.sub.2 and N.sub.2 plasma, give dielectric/GaAs interfaces with a midgap density of interface states well below 10.sup.11 cm.sup.-2 eV.sup.-1.
It is therefore an object of the invention to provide stoichiometric gallium oxide thin films with dielectric properties on semiconducting, insulating and metallic substrates, in particular on III-V semiconducting substrates.